The development of effective hydrogen storage technologies remains a key technical challenge to the widespread use of hydrogen fuel cell vehicles and devices. Both metal hydrides and carbon materials have been studied as promising hydrogen storage materials. However, higher capacity metal hydrides, such as magnesium hydride, are limited by their slow kinetics and require operating temperatures above 300ºC. While carbon materials show fast adsorption and desorption kinetics, at room temperature or higher carbon materials alone cannot achieve significant hydrogen capacity. Recently, the addition of carbon nanostructures to magnesium, via ball milling, has been reported to improve kinetics and dehydrogenation temperatures. In this study we investigated the preparation and hydrogen adsorption properties of magnesium loaded on an activated carbon fibre (ACF). The decomposition magnesium chloride, MgCl2, impregnated on ACF was observed by thermogravimetric analysis (TGA) under nitrogen and hydrogen atmospheres to identify process conditions for synthesis of Mg loaded ACF. The rate of hydrogen adsorption on ACF loaded with 11.2 %wt Mg was measured using a volumetric method at a temperature of 300ºC and hydrogen pressure of 2.2 MPa. The adsorption was compared to that on a bulk Mg powder at the same conditions. While hydrogen uptake on both samples was slow, the Mg loaded ACF sample did adsorb hydrogen suggesting the successful synthesis of Mg particles, and not MgO, on the ACF surface. Hydrogen uptake on a magnesium weight basis was 4.0 %wt H2/Mg for the Mg loaded ACF compared to 1.9 %wt for the bulk Mg powder.